The long-range goal of the research is to foster development of better approaches to overcome the devastating problems of tissue loss and organ failure. The objective of this proposal is to determine how specific micro-structural and mechanical properties of a 3D extracellular matrix (ECM) define the distribution and transfer of mechanical signals to cells that in turn regulate their response and ultimately contribute to the overall tissue structure/function. The central hypothesis for the research is that the cellular response to micro-structural composition and micro-mechanical loading within a 3D ECM is mediated, in part, by the distribution and composition of cell-matrix adhesions. The rationale for the research is that definition of critical 3D structural and mechanical features of a cell's ECM environment, especially at the micro level, as well as identification of the mechanisms by which they influence cell behavior will make it possible to engineer biomaterials with specific material properties that predictably induce a cellular response that accelerates or improves tissue restoration. The objective of the proposed research will be achieved by pursuing three specific aims: 1) determine the morphological, phenotypic, cell-matrix adhesion, and ECM remodeling properties of fibroblasts within 3D ECMs in which the micro-structure is quantified and controllably varied and no external mechanical loads are applied; 2) determine the morphological, phenotypic, cell-matrix adhesion, and ECM remodeling properties of fibroblasts within 3D ECMs in which the micro-mechanical properties (e.g., 3D micro level stress and strain fields) are quantified and controllably varied by application of external mechanical loads; and 3) identify mechanisms by which fibroblasts perceive the micro-structural composition and micro-mechanical state of the surrounding 3D ECM. Expertise in the areas of ECM biochemistry, cell biology, biomechanics, and bioimaging will be combined to yield the following outcomes. First, specific structural-mechanical attributes of a cell's ECM micro-environment will be quantitatively defined. In turn, the dependence of the cellular response on specific micro-structural and mechanical properties of a 3D ECM will be established in the presence and absence of externally applied mechanical loads. Third, the effect of other major cellular signals on the ability of cells to sense and response to these biophysical cues will be determined. Fourth, key events associated with celI-ECM adhesion that provide cells with the ability to sense and respond to physical properties of a 3D ECM microenvironment will be identified. Collectively, these outcomes will provide new information regarding the physical aspects of celI-ECM interaction and establish the role of cell-matrix adhesions in the ability of cells to respond to 3D structural and mechanical cues provided by the ECM. This research is significant to tissue engineering and medicine because the results are expected to define much needed fundamental principles and design criteria that will lay the foundation for directed repair of damaged tissues.